A compound archery bow includes a bow string operative in conjunction with a set of particularly configured pulleys, and one or more bow cables. In a typical compound bow, the pulleys (also termed cams) are configured so that when the bow string is drawn, the cables are wound into grooves on the pulleys, thereby decreasing their effective length, and storing energy in the bow. In a bow of this type, the force required to displace the bow string (i.e. the draw force) varies as a function of the draw length, and this is termed the force/draw profile. In a typical compound bow, the force/draw profile is selected so that, initially, a relatively high level of force is required to displace the bow string, and thereafter the force required for further displacement decreases. This decrease is termed “drop off” and allows for the bow to be held at full draw with a minimized force. The force/draw characteristics of a compound bow allow storage of a high degree of mechanical energy resulting in higher velocity and a flatter path of travel for the arrow. An early design of compound bows is shown in U.S. Pat. No. 3,486,495.
Most compound bows include two specialized pulleys (also referred to as cams), and it is necessary to ensure that the two pulleys operate in synchrony. This is referred to as timing or balance. If a bow is out of balance, uneven forces can be applied to the bow string compromising accuracy. As will be explained in detail hereinbelow, the present invention provides for a pulley system for archery bows which is inherently self-balancing. This self-balancing pulley assembly is referred to by the inventor hereof as the “Libra” assembly, and trademark rights are claimed therein. In addition to being self-balancing, the Libra self-balancing pulley assembly provides for an improved force/draw profile wherein an increased amount of energy may be stored in the bow during the initial portion of the draw cycle. As will be further described, the pulley assembly includes a uniquely configured design of pulley which may be used with a like pulley, or with pulleys of other design.